A. Field
Embodiments described herein relate generally to radiation therapy equipment having a multi-divided irradiation collimator that can accurately determine an irradiation field of radiation as similar to a configuration of a desired region on an object.
B. Background
Typically, the radiation therapy equipment has an irradiation head unit for irradiating radiation on an object. In the irradiation head unit, an irradiation collimator (i.e., radiation collimator) is installed to determine an irradiation field on a desired treatment target region, such as a malignant tumor region of an object for preventing a radiation hazard from unnecessary radiation regions on the object. To reduce the radiation hazard as much as possible, it is required for the irradiation collimator to determine the irradiation field as accurately as possible to a configuration of the target treatment region. Usually, the irradiation collimator is comprised of an upper pair of collimator blocks provided at a near side of a radiation source along the radiation axis and a lower pair of collimator blocks provided at a lower position than the upper pair of collimator blocks along the radiation axis. The lower pair of collimator blocks is positioned so as to orthogonally cross the upper pair of collimator blocks.
The pair of upper collimator blocks is provided so as to face with each other with centering an irradiation axis of the radiation. The pair of upper collimator blocks is driven so as to approach or get away from each other along an arc shaped tracking direction (X-direction). The arc is a portion of a circle with centering the radiation source. The pair of lower collimator blocks is also provided so as to face with each other with centering an irradiation axis of the radiation. The pair of lower collimator blocks is driven so as to approach or get away from each other along an orthogonal arc shaped tracking direction (Y-direction) to the X-direction for tracking by the upper collimator blocks. Each of the lower collimator blocks is comprised of a multi-divided collimator block that is constructed by a plurality of closely attached leaf plates.
Each of the plurality of leaf plates has an arc shaped tracking surface facing the radiation irradiation axis and a toothed configuration of a screw is provided on the tracking surface in order to engage with a driving gear. The driving gear is fixed to a tip portion a rotation shaft. The shaft is rotated by a motor of a driving source through a driving power transmitting mechanism such as worm gears. A detection unit, such as a potentiometer or an encoder is provided to detect a driven amount of the gears. Based on the data detected by the detection unit, each of the leaf plates in the lower collimator blocks is independently driven to a desired position.
Thus, in a conventional radiation therapy equipment, an irradiation field is formed so as to be approximate to an irregular shape of a target treatment region by moving the pair of upper collimator blocks in the X direction and each of the plurality of leaf plates in each of the pair of lower collimator blocks in the Y direction being orthogonal to the X direction.
However, the conventional irradiation collimator needs to use the driving power transmitting mechanism to rotate a driving gear through a shaft by transmitting a driving power of a motor to independently move each of the plurality of leaf plates in the lower collimator block. Since the conventional driving power transmitting mechanism is constructed by combining various types of toothed wheels, backlash due to the respective toothed wheels are accumulated, it has difficult to accurately control to position each of the leaf plates in the irradiation collimator.
Further, in the conventional irradiation collimator, the driving power transmitting mechanism needs to be provided so as that the motor must be positioned in parallel or at a right angle to the rotation shaft for each of the leaf plates. Due to such a limitation, it has been difficult to increase the number of the shaft driving power transmitting mechanism to increase the number of the leaf plates in a limited space of the irradiation head unit.
Recently, to protect against radiation hazards, a requirement for setting an irradiation field as accurately close to a configuration of a target treatment region is strongly increased. To set the irradiation field as closely as possible to an irregular shape of the target treatment region, the number of the leaf plates in the lower collimator blocks needs to be increased with decreasing each thickness of the leaf plates. However, as mentioned above, it has been difficult to increase the number of the shaft driving power transmitting mechanisms to increase the number of the leaf plates in a limited space of the irradiation head unit.